Influence of collars on reduction in scour depth at two piers in a tandem configuration

Bridge failure, due to local scour at bridge pier foundations, has become a critical issue in river and bridge engineering, which might lead to transportation disruption, loss of lives and economic problems. A practical solution to prevent bridge collapses is the implementation of scour mitigation methods around bridge foundations. Based on an experimental perspective, this study is focused on the influence of the size and position of circular collars from the sediment bed on scour depth at two tandem piers. To meet this end, long-lasting experiments are performed under clear-water conditions using uniform sand for bed materials. Compared to the adjacent position of the collar on the bed, placing the collars below the bed would increase the delay time of scour at the piers up to four times. However, regardless of the delay time, the observations indicate that locating the collars on the initial bed surface results in maximum reduction in scour depths around the piers. It was found that diminishing the flow intensity has a dramatic impact on the scour reduction at the piers, so that maximum reduction in scour depths at piers increased on average from 20 to 70% with the reduction in the flow intensity from 0.95 to 0.9

The performance of collars on scour reduction at tandem piers aligned with different skew angles

Local scouring is a leading cause of bridge collapses. To protect bridges against local scouring, different countermeasures have been proposed and tested in the literature. In this study, the performance of collars was evaluated for scour reduction at two tandem piers aligned with four skew angles () of with respect to flow direction. For this purpose, long duration tests were conducted with uniform sediments under clear-water conditions with flow intensities close to the threshold of sediment motion. The results showed that increasing the skew angle increased the scour depth, while the performance of collars for scour reduction decreased. The maximum and minimum scour depths occurred at skew angles of and respectively, around both the piers with and without collars. Analysis of the results indicated that the maximum scour depth at the upstream pier shifted to the downstream pier from and for the tandem piers with and without collars, respectively. In addition, as the skew angle increased, the equilibrium time of scour increased. Moreover, the performance of collars for scour reduction around the piers decreased over time

Analysing supply chain coordination mechanisms dealing with repurposing challenges during Covid-19 pandemic in an emerging economy: a multi-layer decision making approach

Following the outbreak of the Covid-19 pandemic, there was a serious need for the pharmaceutical industry to combat the disease more quickly and effectively. In this regard, numerous companies set out to repurpose current drugs. The noticed decision has major challenges in various dimensions, including the creation and management of an efficient supply chain. The present study attempts to examine the significance and relationships of the repurposing challenges and analyze the effectiveness of supply chain coordination contracts confronting them. In this regard, a combination of Decision-Making Trial and Evaluation Laboratory (DEMATEL) and Analytic Network Process (ANP) named DANP method is applied to investigate the relationships and extracting the weights of the mentioned challenges and the multi-criteria optimization and compromise solution technique called VIKOR is employed to prioritize the supply chain coordination contracts found on their impact facing with repurposing challenges. The mentioned techniques have been conducted under the condition of linguistic Z-numbers. The results demonstrated that financial support and digitalization are the most influential challenges. Moreover, collaboration and data availability have the most weight. In addition, four contracts including effort sharing, cost-sharing, credit option and buyback are the best contracts that companies in the merging economy of Iran should concentrate on them. This research proposes a novel framework of decision-making by integrating DANP and VIKOR with linguistic Z-numbers. Additionally, this study takes a new look at the use of coordination contracts from the viewpoint of repurposing challenges which is highlighted particularly during the Covid-19 pandemic.</p